Roland Griffiths was trying to meditate – but he couldn’t do it. If he sat there for a few minutes, it felt as through hours were stretching out before him, like a long, slow torture. So he quit. This tall, thin young scientist, who was rapidly rising through the ranks of academic psychology, would not meditate again for twenty years — but when he returned to mindfulness, he became part of unlocking something crucial. Professor Griffiths was going to make a breakthrough — just not for himself, but for all of us.

I came to Roland Griffiths’ door towards the end of a 40,000-mile journey, from Sydney to Sao Paulo to San Francisco. I set out on this trek to interview the world’s leading experts on what causes depression and anxiety, and what really solves them, because I had been downcast and acutely anxious for much of my life, and the solutions I had been offered up to then hadn’t taken me very far.

Everywhere I went for my book "Lost Connections: Uncovering The Real Causes of Depression – and the Unexpected Solutions," I heard people talking excitedly about the new research into psychedelics that was slowly creaking open. Until the mid-1960s, many reputable scientists had set up clinical trials where they gave these drugs — either plants or synthetic chemicals which induce an altered mental state – to people suffering from depression, alcoholism, and other problems. They had some quite striking early findings – and then, in a cultural panic, the research was slammed shut by the Nixon administration.

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And then came Roland Griffiths.

* * *

Professor Griffiths had been a young grad student when he walked away from his attempts at meditation, pissed off. As the years passed, he rose to become a leading Professor of Psychology at Johns Hopkins University School of Medicine in Maryland, one of the best academic institutions in the world. He rose, he says, by being “certifiably workaholic,” or “pretty close to it.” He became the leading expert in the world on the effects of caffeine, and he was like a personification of his drug: wired, and tightly-wound. He was succeeding on all the measures of success in his world – but he felt like there was a hole in his life. It was, he told me “as though in some respects I was going through the motions of being a scientist and having a career in science.” He found himself thinking back across the decades, to his aborted stab at mindfulness. He started to look to see if there was any scientific evidence for the benefits of mindfulness – but he quickly saw that in his academic world, it was almost heresy to talk about the deep inner self. This was not regarded as real science.

He went to an ashram – and found that this time, he could meditate after all. “This inner world started to open up — and I started to open up,” he said. The people he was meeting who had been meditating for years seemed — as he observed them — to have a spiritual dimension to their lives that really benefited them in all sorts of ways. They appeared calmer, and happier, and less anxious.

So Roland started to ask himself some basic questions. What is happening when a person meditates? If you meditate in a dedicated way, for long enough, most people say that they start to experience a spiritual change. Why did meditation make people feel they were being changed in a way that was mystical — and what did that even mean? He stumbled across the psychedelics studies from the 1960s, and it seemed to him that the way people described feeling when they took psychedelics was very similar to the way people described when they were in a state of deep meditation. He began to wonder if they were, in some strange sense, two different ways of approaching the same insight. Could investigating one unlock the secrets of the other?

So he did something bold. He applied to conduct the very first clinical trial on a psychedelic since the ban a whole generation before. He wanted to give psilocybin, a naturally occurring chemical found inside “magic” mushrooms, to “respectable” citizens who had never used it before, to see if they would have a mystical experience — and to discover what the longer-term consequences, if any, would be.

“I have to say, frankly, that I was a skeptic,” he told me one afternoon as we drove across Baltimore. When he got the permission to proceed, people were startled. They assumed it was because the regulators thought Roland, with such a solid reputation, could only find that these drugs were harmful.

So dozens of ordinary professional people were recruited in Maryland. We want you, the advertisements said, to do something unusual.

* * *

Mark didn’t know what to expect as he walked into Roland’s lab. It had been decorated to look like a living room in an ordinary home, with a sofa, and soothing pictures on the wall, and a carpet. He was a straight-laced forty-nine-year-old financial consultant who had never taken a psychedelic before; he hadn’t even smoked cannabis.

He responded because he had become divorced from his wife a few years earlier and become depressed. He had been taking an antidepressant for four months, but it was just making him feel sluggish. Now he was worried about himself. He felt he kept everybody at arm’s length, and never really connected to them.

This had begun when Mark was ten years old and his father had developed a heart problem — a defect in one of his valves. One day he suddenly started experiencing terrible pain, and as Mark watched him get into the ambulance, he knew instinctively he would never see his father again. In the months and years that followed, Mark’s mother was so lost in her own grief that she couldn’t discuss the death with the boy, and nobody else did, either. “I think I just stuffed it all. I think I just went into denial mode,” Mark told me. It was the beginning of a pattern for him — of hiding, in order to protect himself.

As he lay on the sofa in the pretend lounge, his anxiety understandably flared. This was to be the first of three sessions in which he was given psilocybin. At the Baptist church he went to, they used to give the teenagers little comic strips about a man who took LSD and thought his face was melting. He couldn’t stop and had to be taken to a psych ward — and never recovered.

He lay down on the sofa, and when he was comfortable, he was handed a small psilocybin pill to swallow. Then, calmly, he looked at some images of landscapes in a book with his guide through the experience, Dr. Bill Richards, and then Bill placed a blindfold over Mark’s eyes and put some headphones on him, playing gentle music. And within forty-five minutes, Mark started to feel something different. “I could feel my mind getting looser,” he said to me.

The scientists had explained to him in the long preparation process that calling these drugs “hallucinogens” is a bit of a mistake. A true hallucination involves seeing something that isn’t there and thinking it’s as real as the device on which you’re reading this article — a physical object in the world. That’s actually very rare. It’s more accurate, they said, to call them “psychedelics”—which in Greek means, literally, mind-manifesting. What these drugs do is draw things out of your subconscious and bring them into your conscious mind. So you don’t hallucinate—rather, you will see things in the same way you see them in a dream, except you are conscious; and at any given moment, you will be able to talk to your guide, Bill, and know he is physically present, and know that the things you are seeing as a result of the drug are not physically there.

“There’s no visual experience of the walls turning or anything like that,” Mark told me. “It’s totally dark. And all you hear is this music as a means of grounding you—and then it’s just internal visualization . . . I would say [it is like] dreaming awake,” except he could remember it all afterward, vividly—“as vividly as anything in my life.”

* * *

As he lay back on the sofa, Mark felt he was paddling in a great cool lake. He started wandering up and down, and he could see there were different coves around him, and that there would be inlets from those coves. He sensed intuitively — as you do in a dream—that this lake symbolized all of humankind. All of us empty out into this lake, he thought — all our feelings, all our longings, all our thoughts.

He decided he was going to explore one of these coves. He hopped from rock to rock, all the way up the stream, and he felt something was calling him to keep going, deeper, deeper. He then reached a sixty-foot waterfall and stood before it in awe. He realized that he could swim up it, and he thought that when he got to the top of the waterfall, he would be wherever he wanted to go in life, and “the answer would be there for me.”

He told Bill, his guide, what was happening. “Drink it in,” Bill said.

When Mark reached the top of the waterfall he saw a little fawn in the water, drinking from the stream. It looked at Mark and said “There’s some unfinished business here for you to take care of,” from your childhood. “This is something that you need to take care of if you want to continue to evolve and grow.”

Now, at the top of this waterfall, Mark felt for the first time in his life that it was safe to approach the grief he had hidden away since he was ten years old. He followed the fawn farther down the river and he found an amphitheater. And there, waiting for Mark, was his dad, as he had been that last time Mark saw him.

Mark’s father explained that he was going to tell him some things he had wanted to be able to say to him for a long time. First of all, he wanted Mark to know that he was fine. “That he had to leave,” Mark recalls, “and he felt bad about it, but [he said] ‘Mark—you are perfect just the way you are, and you have everything you need.’”

Mark cried when he heard that, in a way he had never cried for his father before. His father held him, and he said: “Mark, don’t hide. Go seek.”

Then, later, Mark met another a smiling guide – a man who had come to help him through this journey, he said. He reached inside him, and he began to pull out a great slew of concrete walls. The guide said: “Mark, we need to talk to this part of you.” The guide said to the walls: “You have done an amazing job for Mark. You have protected him. You have created incredible works of art for him—these beautiful walls you created for Mark, these trenches, this scaffolding which has protected Mark for many, many years and got him to this place. We need to make sure you’re okay with taking these [walls] down so you can experience what’s next.”

“And it was done with such love,” Mark told me. “No judgment.’” And the frightened parts of Mark consented to let his walls come down. And as he did, Mark realized that close by, he could see people he had loved, who had died—his father, and his aunt—applauding him.

Mark knew then—“this whole journey, everything I had experienced, this whole push, was to say—life is for living. Go out and live. Go out and explore, and enjoy, and just take it all in.” He had an intense sense of the beauty of being alive, of being human—“the magnificence of it, the wisdom of it, it was just overwhelming.”

And then he began to feel the drug wearing off, and it was “like you were back in your own ego,” as he puts it. He had arrived at Johns Hopkins at nine o’clock, and he left at five thirty. When his girlfriend, Jean picked him up, she asked him how it had gone, and he had no idea what to say.

* * *

In the months that followed, Mark found he was able to talk about his father in a way he never had before. He had a strong sense that “the more open I am, and the more revealing I am, the more I’m going to get from anything.” He felt his anxiety had—to a significant degree—been replaced with a sense of wonder. “I felt I was able to be a little bit more human with people,” and he even started to go to ballroom dancing with his girlfriend, something he would have had to be dragged to kicking and screaming before.

* * *

Part of the job for Roland — the skeptical scientist who was running this experiment — was to interview everyone who had been given psilocybin, two months after the experience. These people would come in, one by one, and their answer was almost always the same. Routinely, they would say it was “one of the most meaningful [experiences] of my life” and compare it to the birth of a child, or the death of a parent. Mark was typical. “It struck me as kind of wildly implausible at first,” Roland said to me. “My immediate thought was — what kind of life experience did these people have [before the experiment]? But they were high-functioning, mostly professional-level people.”

Some 80 percent of people like Mark still said, two months later, that it was one of the five most important things that had ever happened to them.

This was the first of many striking results they found when they gave psylocibin to patients. They tried administering it to long-term smokers who had tried everything to give up. Incredibly, 80 percent of them quit, and remained non-smokers a year later. To give a comparison point: the next most successful tool for quitting smoking, nicotine patches, works for 17 percent of people. This has opened up an array of studies currently looking at whether it can help with other forms of addiction.

Roland’s work played a key role in re-opening the gates of psychedelic research across the world. I also traveled to interview the scientists who have done this work in Los Angeles, New York, London, Sao Paulo, and Oslo. They have all made startling discoveries. For example, a team working at University College London gave psilocybin to people who had severe depression and hadn’t been helped with any other form of treatment. It was only a small preliminary study without a control group, so we shouldn’t overstate it, but they found that nearly 50 percent of patients saw their depression go away entirely for the three-month period of the trial.

So what, I wanted to know, is happening here?

* * *

Whatever is happening, all the scientists involved warned that people should not lightly decide to try these experiences. If meditation is the beginners’ ski-slope, Dr Bill Richards told me, psychedelics are the Olympic slopes. They should only be tried in carefully monitored circumstances, where you can be monitored by people with deep experience.

* * *

I learned that within all this research, there are two smaller findings – ones that I think begin to tell us what is really going on here. They show us the power of these substances – and their limitations. At first glance, they will seem a little strange.

Here’s the first one. When you take a psychedelic, most people will have a spiritual experience – you get a sense that your ego-walls have been lowered, and you are deeply connected to the people around you, to our whole species, to the natural world, to existence. But it turns out the intensity of the spiritual experience varies from person to person. For some people, it will be incredibly intense; for some people, mild; and some people have no spiritual experience at all. At Johns Hopkins, the team discovered that many of the positive effects correlate very closely with the intensity of the spiritual experience. So if you had a super-charged spiritual experience, you got the benefits very heavily; and if you had no spiritual experience, you didn’t have many positive effects.

Johann Hari’s book, "Chasing The Scream: The First and Last Days of the War on Drugs" is published by Bloomsbury as a hardback, ebook and audiobook. Find out more about the book or follow Hari on Twitter @johannhari101.